nice error message

src/lib.rs

@@ -1,7 +1,6 @@
 use clap::Parser;
-use std::fmt::Debug;
+use std::fmt::{Debug, Formatter};
 use std::fs;
-use std::io;
 use std::path::PathBuf;
 
 #[derive(Parser, Debug)]
@@ -27,7 +26,17 @@ pub struct Cli {
     ignore_extras: bool,
 }
 
-pub fn skip<F>(cli: &Cli, out: F) -> io::Result<()>
+pub struct SkipError(String);
+
+impl Debug for SkipError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::result::Result<(), std::fmt::Error> {
+        write!(f, "{}", self.0)
+    }
+}
+
+pub type Result<T> = core::result::Result<T, SkipError>;
+
+pub fn skip<F>(cli: &Cli, out: F) -> Result<()>
 where
     F: FnMut(String) -> (),
 {
@@ -41,11 +50,11 @@ where
                 skip_file_lines(cli, out, file)
             }
         }
-        None => todo!("reading from stdin"),
+        None => Err(SkipError("Not yet implemented - reading from stdin".into())),
     }
 }
 
-fn skip_file_lines<F>(cli: &Cli, mut out: F, file: &PathBuf) -> io::Result<()>
+fn skip_file_lines<F>(cli: &Cli, mut out: F, file: &PathBuf) -> Result<()>
 where
     F: FnMut(String) -> (),
 {
@@ -60,7 +69,7 @@ where
     Ok(())
 }
 
-fn skip_file_lines_matching<F>(cli: &Cli, mut out: F, file: &PathBuf, line: &str) -> io::Result<()>
+fn skip_file_lines_matching<F>(cli: &Cli, mut out: F, file: &PathBuf, line: &str) -> Result<()>
 where
     F: FnMut(String) -> (),
 {
@@ -77,7 +86,7 @@ where
     Ok(())
 }
 
-fn skip_file_tokens<F>(cli: &Cli, mut out: F, file: &PathBuf, token: &str) -> io::Result<()>
+fn skip_file_tokens<F>(cli: &Cli, mut out: F, file: &PathBuf, token: &str) -> Result<()>
 where
     F: FnMut(String) -> (),
 {
@@ -105,7 +114,7 @@ mod tests {
     use super::*;
 
     #[test]
-    fn skip_one_line() -> io::Result<()> {
+    fn skip_one_line() -> Result<()> {
         //given
         let cli = Cli {
             lines: 1,
@@ -125,7 +134,7 @@ mod tests {
     }
 
     #[test]
-    fn skip_two_lines() -> io::Result<()> {
+    fn skip_two_lines() -> Result<()> {
         //given
         let cli = Cli {
             lines: 2,
@@ -145,7 +154,7 @@ mod tests {
     }
 
     #[test]
-    fn skip_two_matching_lines() -> io::Result<()> {
+    fn skip_two_matching_lines() -> Result<()> {
         //given
         let cli = Cli {
             lines: 2,
@@ -165,7 +174,7 @@ mod tests {
     }
 
     #[test]
-    fn skip_three_matching_tokens() -> io::Result<()> {
+    fn skip_three_matching_tokens() -> Result<()> {
         //given
         let cli = Cli {
             lines: 3,
@@ -192,7 +201,7 @@ mod tests {
     }
 
     #[test]
-    fn skip_three_matching_tokens_include_extras() -> io::Result<()> {
+    fn skip_three_matching_tokens_include_extras() -> Result<()> {
         //given
         let cli = Cli {
             lines: 4,
@@ -224,7 +233,7 @@ mod tests {
     }
 
     #[test]
-    fn skip_three_matching_tokens_ignore_extras() -> io::Result<()> {
+    fn skip_three_matching_tokens_ignore_extras() -> Result<()> {
         //given
         let cli = Cli {
             lines: 4,

src/main.rs

@@ -1,8 +1,8 @@
 use clap::Parser;
-use skip::{skip, Cli};
+use skip::{skip, Cli, Result};
 use std::io::Write;
 
-fn main() -> std::io::Result<()> {
+fn main() -> Result<()> {
     let cli = Cli::parse();
 
     let stdout = std::io::stdout();